Increasing efforts to miniaturize have resulted in the need to construct microstructures in thin films. One example is in the area of constructing write heads for magnetic storage media.
Write heads are used in disk and tape storage systems to generate a magnetic signal corresponding to information to be stored on the disk or tape. Top poles form a portion of an inductive element that converts an electrical pulse into a magnetic pulse. The magnetic pulse writes a transition in magnetic media on the disk or tape. Top poles are constructed from magnetic materials such as, for example, cobalt-zirconium-tantalum (CZT).
In order to increase the data density of disk and tape storage systems, write tracks are narrowed. This requires a corresponding decrease in the write track line widths defining top poles. As the width decreases, the tolerance on dimensions also decreases. Producing smaller structures with tighter dimensions in CZT has driven the need to develop thin film manufacturing processes with increased precision.
One method for etching thin film material, such as CZT top poles, is to use a wet etch process. In wet etching, a mask layer is deposited over regions that are not to be etched. The assembly is then exposed to a wet etchant. The etchant dissolves material not protected by the mask. A difficulty with wet etching is that the etchant dissolves some material underneath the mask. Hence, wet etching cannot achieve the tolerances required for smaller write tracks.
Another method for etching thin film structures such as CZT poles is ion milling. In ion milling, argon (Ar) is used to remove material in unmasked areas. Ion milling has the advantage that, if conditions are appropriate, a near vertical etch can be obtained. One difficulty with Ar ion etching is that the mask is also etched away. Since there is a limit to how thick a typical photoresist mask can be applied using common manufacturing methods, the photoresist mask limits the thickness of the resulting structure.
What is needed is a method for masking and etching microstructures, in particular CZT top poles, that allows ion milling to be used for achieving desired tolerances with the desired microstructure thickness.